Immunofluorescence assays (IFAs) have identified antibodies related to the recently discovered sixth human herpes virus (HHV- 6, formerly HBLV) in both healthy and sick individuals. IFAs for detecting antibodies are difficult to standardize and estimates of HHV-6 infection rates have varied widely. The long-term objectives of the project described here are to develop a sensitive, specific, and reproductible test for HHV-6 antibodies and to develop monoclonal antibodies (MoAbs) specific for HHV-6. Specifically, two enzyme adsorbent assays (EIAs) will be developed for antibody testing. The first EIA will be a refined version of the EIA developed during Phase I which used microplates coated with HHV-6 virions. The second EIA will use microplates coated with HHV-6 structural antigens which have been immunoaffinity purified with MoAbs developed in this project. MoAbs developed will include not only those specific for the virus structural antigens produced late in the virus replication cycle, but also those specific for antigens produced early in infection. The second EIA and the MoAbs will be prepared for commercial distribution to researchers to aid them in studies on the role of HHV-6 in human disease.